1. Field
The present application generally relates to integrated circuit (IC) metrology, and, more particularly, to the use of virtual profile libraries or virtual profile data spaces to determine the critical dimensions (CD's) and profiles of IC structures.
2. Description of the Related Art
With the current drive towards smaller geometries of IC features, features measurement is increasingly difficult as the size of the features become smaller. However, knowledge of the dimensions of gratings or periodic structures is essential in order to determine if the dimensions of the features are within the acceptable ranges and if a particular fabrication process causes the sidewalls of the features to be tapered, vertical, T-topped, undercut, or have footings.
Traditionally, a sample was cleaved and examined with a scanning electron microscope (SEM) or similar device. The cross-section SEM method is typically slow, expensive, and destructive whereas the CD SEM method only provides one measurement number seen from the top of the feature. Spectroscopic reflectometry and ellipsometry are used to beam light on the structure and measure the spectrum of reflected signals. Current practices basically use an empirical approach where the spectra of reflected light is measured for a known width of features in a structure. This process is time consuming and expensive even for a limited library of profiles of structure dimensions and the associated spectrum data of reflected/diffracted light. Furthermore, if such a library were built for a wide range of profiles at a fine resolution, the process of building the library is time consuming and cost-prohibitive. With IC features becoming smaller, there is a need for a library with even finer resolution. As the resolution of the library increases, the size of the library increases while the time to create the library increases exponentially. Furthermore, an extensive library of profiles and spectra is inefficient for searching purposes, especially for real-time work. Thus, there is a need for a method, system, and/or apparatus that facilitates the use of metrology devices and systems for measuring profiles without creating huge profile libraries or data collections and incurring extensive searches of said profile libraries or data collections.